Review articleTechnology Advances to Improve Response to Cardiac Resynchronization Therapy: What Clinicians Should KnowAvances tecnológicos para mejorar la respuesta ventricular en la resincronización cardiaca: lo que el clínico debe conocer
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INTRODUCTION
Cardiac resynchronization therapy (CRT) is a well-established nonpharmacological treatment for symptomatic heart failure (HF) patients with reduced left ventricular ejection fraction (LVEF), prolonged QRS duration, and abnormal QRS morphology. As recently reported by the ALTITUDE registry,1 the improved outcome of CRT patients observed over the last decade is related to greater adherence to pharmacological therapy and device therapy as recommended by clinical practice guidelines.2, 3 According
IMPORTANCE OF THE LV QUADRIPOLAR LEAD, AND LV MULTIPOINT PACING
Several studies have confirmed the importance of targeting a late activated electrical/mechanical area of the left ventricle for LV pacing.5, 6 The design, shape and characteristics of LV pacing leads have considerably evolved during the past decades, driven by the clinical need to match a wide variety of cardiac vein anatomies while ensuring high mechanical stability and electrical performance. Left ventricular leads evolved from a single-electrode lead to the current quadripolar-electrode
BEYOND CONVENTIONAL DELIVERY OF CRT
In the most recent years, a number of physiological considerations have challenged the concept of traditional delivery of CRT. The first of these concepts–LV endocardial pacing–is based on the observation that conventional CRT is delivered by placing a pacing lead at the endocardium of the right ventricle and one lead on the epicardial LV wall. This pacing configuration thus reverses the physiological LV activation (ie, from endocardium to epicardium).18, 19 The second concept–His bundle
HOW CAN WE IMPROVE THE RESPONSE TO CRT?
Among several factors that could adversely affect the response to CRT, suboptimal optimization of the AV delay and VV timing of the CRT device represents the most common–and supposedly the most readily correctable–variable.27 Several studies have demonstrated the acute hemodynamic benefits of optimization of AV and VV timings.28 Although echocardiography-guided optimization is an easily accessible method, it nevertheless remains a logistical challenging and resource-intensive process, with the
THE BURDEN OF ATRIAL FIBRILLATION
Although AF occurs in more than 25% of eligible CRT patients, the available evidence of benefit from CRT in patients with any type of AF is limited to observational trials or to registry data. The prognosis of HF patients with AF is generally worse than that of patients in sinus rhythm,34 and therapy with beta-blocking agents–although effectively reducing heart rate–does not impact on mortality.35
The use of CRT in HF patients who are either at risk of developing AF or already have a history of
SHOCK-REDUCING STRATEGIES IN PATIENTS WITH CRT WITH DEFIBRILLATION
The occurrence of both appropriate and inappropriate implantable cardioverter-defibrillator (ICD) shock is associated with a subsequent 3- to 5-fold increased risk of death among patients with primary prevention ICDs.45 Interventions aiming to reduce the number of shocks consist of the administration of antiarrhythmic drugs, device-programmed arrhythmia terminating algorithms, and ablation strategies. Data from the MADIT-CRT trial (Multicenter Automatic Defibrillator Implantation with CRT)
THE PREDICTION OF EPISODES OF HEART FAILURE
The prediction of episodes of HF decompensation is an important goal from a patient's, physician's and health care economics perspective. Most of the risk scores used so far to identify patients at risk for the development of HF or mortality, assess a static risk at baseline or in an in-hospital setting. In contrast, implantable medical devices such as pacemakers, ICDs, and CRTs can provide daily measurements of multiple “diagnostic” parameters for possible evaluation of patients’ clinical
CONCLUSIONS AND FUTURE PROSPECTS
The recognition by Carl Wiggers more than 90 years ago that conduction disturbances lead to LV dysfunction54 can be traced to experiments that provided the paradigm for CRT.55 Pacemaker technology, designed to correct ventricular conduction disturbances, was eventually tested in randomized, controlled CRT trials, driven by engineers, clinicians, and the industry. As probably in other fields of cardiology, technology and innovations for CRT delivery have been at the forefront in
CONFLICTS OF INTEREST
A. Auricchio is a consultant to Medtronic, Boston Scientific, Biosense Webster, and LivaNova and has received speaker's fees from Medtronic, Boston Scientific, and LivaNova.
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